Re: [PATCH] block: avoild hang when bio_list is non-NULL in submit_bio_wait()

[Jiucheng Xu <jiucheng.xu@amlogic.com>]

On 3/2/2026 10:23 PM, Gao Xiang wrote:
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> Hi Christoph,
> 
> On 2026/3/2 21:50, Christoph Hellwig wrote:
>> On Mon, Mar 02, 2026 at 10:51:03AM +0800, Jiucheng Xu via B4 Relay wrote:
>>> From: Jiucheng Xu <jiucheng.xu@amlogic.com>
>>>
>>> When current->bio_list is non-NULL in submit_bio_wait(),
>>> submit_bio_noacct_nocheck appends bio to bio_list but skips IO
>>> submission, causing submit_bio_wait() to hang indefinitely.
>>>
>>> Fix this by temporarily backup bio_list, setting bio_list to
>>> NULL before calling submit_bio(), then restoring bio_list
>>> after submit_bio() returns.
>>
>> No.  Fix this by not doing something that is a bad idea.
>>
>>> I've trimmed down the call stack, as follows:
>>>
>>> f2fs_submit_read_io
>>>    submit_bio
>>>      mmc_blk_mq_recovery
>>>        z_erofs_endio
>>>          vm_map_ram
>>
>> ->bi_end_io code really should not be having random in_atomic()
>> checks that make it completely different, but even if they have
> 
> Thanks for the head-up.
> 
> For this part, I'm pretty sure we need this particular one
> otherwise the scheduling performance (latency sensitive)
> is unacceptable for all Android phone users.
> 
>> that need to use GFP_NOIO.
> 
> Yes, it should make vm_map_ram() in the end_io path use
> GFP_NOIO instead.
> 
> Jiucheng, could you add memalloc_noio_{save,restore}() to
> wrap up this path?

Thanks for Christoph's and Xiang's comments, I will try it. Thanks!

Best Regards,
Jiucheng